


From theory to practice

by opposablethumbs



Category: The Avengers (Marvel Movies)
Genre: Avengers: Endgame (Movie) Spoilers, For Science!, Gen, Meta
Language: English
Status: Completed
Published: 2019-04-25
Updated: 2019-04-25
Packaged: 2020-01-31 20:42:24
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 939
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18599044
Author URL: https://archiveofourown.org/users/opposablethumbs/pseuds/opposablethumbs
Summary: Chapter 1 is my attempt at explaining a key premise of Endgame.Chapter 2 is a brief 'missing scene' fic from the end of the movie between Steve and Bucky, based on the above theory.I cannot stress more, this contains spoilers for Endgame.





	1. So Back to the Future lied?

**Author's Note:**

> Chapter 1 is my attempt at explaining a key premise of Endgame.  
> Chapter 2 is a brief 'missing scene' fic from the end of the movie between Steve and Bucky, based on the above theory.
> 
> I cannot stress more, this contains spoilers for Endgame.

**Summary for the Chapter:**

> Right, I've had a couple of hours sleep and I think I've cracked time travel...

The key bit is where they have the whole discussion about creating a paradox, and the fact that in marvel time travel you can't have them. And Scott is like... Back to the future is a lie?

The theory of space-time-reality that they're using (and it's is a legit theory, the math of which is above my paygrade) is that time is non-linear. There is no such thing as past, present and future until passed through the linear filter of human perception. If the individual experiences 1945 AFTER 2019, then events in 1945 can't change 2019 for that person, because - in their perception of time - 2019 has already happened. What the actions in 1945 would do is spawn divergent realities.

So, now we have many Steves. However, it's a function of indeterminacy that while something can be in more than one state if it's unobserved, it can only be one thing under observation. Our observation is of our Steve's timeline, with Bucky having been TWS and therefore - until we switch POV - we can't experience those other timelines. It's therefore perfectly reasonable to assume that Steve's first action in 1945 would be to rescue Bucky and yet us not be able to see the outcome of that. The very final shot of him and Peggy dancing is likely one of those divergent realities where a Steve HAS fixed everything and can be truly happy. And when he makes it back to 2024 (or whatever date we're assuming '5 years later' gives us), only a few moments have passed for Bucky, and all that's changed for him is Steve is now suddenly old. Although I disagree with Steve aging in a normal way for serum reasons, it's at least an easy fandom fix.

Now if this IS the branch of theoretical physics they're clinging to, they are asking a hell of a lot of a general audience. And honestly, one of my big bugbears in professional writing is this need to make it inaccessible to prove you are The SmartTM. Using time travel this way does kind of feel like a condescending pat on the head and being told just to accept it. I accept nothing. That's why I now have a headache. But hopefully, this explanation can bring a little peace to those who are feeling short changed on Steve's characterisation.

**_So tl;dr._ **

The first thing Steve did in the past was rescue Bucky. But it's impossible for us to see the effects of that that if we're tied into our Steve's pov, because the moment he did it, he spawned a new reality that is beyond his (and therefore our) perception of time. If we switch POV (ie fanfic) we can access any of those divergent realities.


	2. A few extra trips around the sun

**Summary for the Chapter:**

> I wrote the conversation I think Steve and Bucky had prior to Steve leaving. Because Bucky clearly knows what to expect, where to look for old Steve and how to tell Sam to go ahead while he hangs back.
> 
> This is written as gen, but you can read stucky, stony, or steggy into it to your heart's content.

**Notes for the Chapter:**

> (Edit 26/04/19 because I watched Endgame again and had more ideas and this has possibly spawned a sequel because fandom is the great enabler and I love you guys.)

Black suits, black tie. Gold cufflinks for the man who most people thought was made only of iron. This was one of the hardest moments of Steve's life, saying goodbye to this person who had given him a home. And it was made all the harder by knowing what he was going to do afterwards.

He heard his door open and close quietly, but the footfalls were so familiar he didn't turn away from doing his tie in the mirror.

"Hey Buck," he greeted.

"You're doing it wrong," Bucky replied of Steve's poor attempt at a Half-Windsor. 

Steve turned round. "You wanna do it for me?"

Bucky huffed but stepped forward, hands going to the silk with familiarity. "I'm still not sure I should be here," he murmured as he passed the material between his flesh and metal fingers.

"Pepper asked you to be," reminded Steve. "Tony did a lot of growing in those five years. Forgave a lot of wrongs. Accepted some of his own."

"You miss him," Bucky said, finishing the tie but his right hand lingering on Steve's shoulder.

Steve looked into Bucky's grey blue eyes, the lines surrounding them. It was now or never. "Buck, I'm going back," he said.

A curious half-smile formed on Bucky's lips. "I know."

It was part of today's events to return the stones to their proper places in time and Steve had asked to be the one who did it. Everyone knew that, and probably assumed it was Steve's sense of duty that made him volunteer. And while Steve could live with that, he couldn't live without telling Bucky the real plan.

"No," he said, "I mean I'm going back and staying." He took a deep breath. "And I promise I won't let what happened happen again. I can't change anything for you, but I can rescue another you, back then. And Peggy. I..." Steve felt tears stinging his eyes, voice breaking under the strain.

Bucky squeezed his shoulder. "Steve, I get it. Shuri explained it to me. Best as she could anyway. When she started on the math, I kinda blanked."

Steve allowed himself a small chuckle. He'd had plenty of moments like that listening to Tony. Bruce. Hell, even Nat from time to time. 

Bucky matched it by allowing his smirk to merge into a soft soft smile. "Just knowing you'll be happy and that... some other me gets a chance?" he said. "It's enough."

The tears spilled, and Bucky dragged him into a hug. "Gonna miss you though, punk," Bucky whispered in his ear.

Steve allowed himself a moment in Bucky's embrace before he pulled away, sniffing and clearing his throat. "I'll be back. You'll not even know I'm gone." He smiled at last, certain this was a promise he would be able to keep. "And for me it'll just be a few extra trips around the sun."


End file.
